Given the pace of virus development, we are probably going to see even nastier criminal attacks in the future.

Some academics have predicted the rise of “cryptoviruses” — malware that invades your computer and encrypts all your files, making them unreadable. “The only way to get the data back will be to pay a ransom,” says Stuart Schechter, a doctoral candidate in computer security at Harvard.

Antivirus companies are writing research papers that worry about the rising threat of “metamorphic” worms — ones that can shift their shapes so radically that antivirus companies cannot recognize they’re a piece of malware.

The profusion of viruses has even become a national-security issue. Government officials worry that terrorists could easily launch viruses that cripple American telecommunications, sowing confusion in advance of a physical 9/11-style attack.